Wheelchair lifts for vehicles are three basic types: 1) floor mounted at the entry sill of a vehicle such as a side or rear door; 2) under floor lifts (UFL) which telescope outwardly from underneath the floor; and 3) under vehicle (frame) lifts (UVL).
The UVL lifts can be distinguished from the UFL, in that while both telescope outwardly from a horizontal stowage bay, the UVL under vehicle lift is located beneath the vehicle frame and must have motion including raising the platform from an intermediate stowage position upwardly to the floor level and downwardly to the ground level. In the UVL, the storage bay is substantially below the floor as it is suspended below the frame and/or axle of the vehicle rather than being above them as in the UFL type lifts.
In contrast, the UFL under floor lift does not lift above stowage level, as stowage takes place at the transfer level at or adjacent to the vehicle floor level. Typically both the UFL and UVL lifts have parallelogram or scissors type mechanisms to raise and lower the platform from the ground level up to the transfer level (the floor level of the vehicle) and, in the UVL, to move to an intermediate storage level.
The floor mounted lifts may be of a variety of types, including dual parallelogram, rotary lifts, and header types employing an inverted U assembly which is pivoted at its upper end, the arms of which carry the telescoping lifting arms. There are a few miscellaneous other types.
A particular problem with both the UVL and UFL type of lifts is that they must telescope beneath either the vehicle floor or its frame, and the lifting scissors or parallelogram must be collapsible and stowable in a relatively small vertical height in the order of 4 to 6 inches. Accordingly, these lifting members are subject to side sway as they drop down or lift. When a wheelchair user gets on the platform, he or she is often not centered. The added weight and motion of the chair on the platform can give rise to sway, which at the very least is disconcerting to the wheelchair user and in worst case situations can cause the mechanism to bind, experience accelerated wear, and possibly fail. This may be exacerbated by off-center location of the load on the platform, as when a vehicle loads or unloads a wheelchair user on an incline, either pointed up or downhill, or when the vehicle is canted to one side as where the roadway has a crown. In addition, the added weight of the wheelchair user on the platform typically causes the vehicle to tilt to that side.
In addition, these mechanisms are relatively complex and require trained service personnel. This puts a significant burden on the transit authority or school district. Accordingly, a lift with a solution to the lateral sway problem and a better lifting assembly would fill a long-felt need in the art.